1. 누락된 인덱스

문제점:

// No index on 'email' field
db.users.find({ email: "user@example.com" })

해결 방법:

// Create index
db.users.createIndex({ email: 1 })

2. 비효율적인 정규식 쿼리

문제점:

// Case-insensitive regex without index
db.users.find({ name: /john/i })

해결 방법:

// Use text index or exact match
db.users.createIndex({ name: "text" })
db.users.find({ $text: { $search: "john" } })

3. 대규모 스킵() 연산

문제점:

// Skipping thousands of documents
db.collection.find().skip(10000).limit(10)

해결 방법:

// Use range queries with indexed field
db.collection.find({ _id: { $gt: lastSeenId } }).limit(10)

4. 불필요한 필드 선택

문제점:

// Fetching entire documents
db.users.find({ status: "active" })

해결 방법:

// Use projection
db.users.find({ status: "active" }, { name: 1, email: 1 })

5. 비효율적인 집계 파이프라인

문제점:

// $match after $lookup
db.orders.aggregate([
  { $lookup: { ... } },
  { $match: { status: "completed" } }
])

해결 방법:

// $match first to reduce documents
db.orders.aggregate([
  { $match: { status: "completed" } },
  { $lookup: { ... } }
])

1. 무제한 배열

문제점:

// Array grows indefinitely
{
  userId: 123,
  activities: [/* thousands of items */]
}

해결 방법:

// Use separate collection or bucketing
{
  userId: 123,
  month: "2024-01",
  activities: [/* limited items */]
}

2. 과도한 임베딩

문제점:

// Deeply nested documents
{
  user: {
    profile: {
      settings: {
        preferences: {
          // many levels deep
        }
      }
    }
  }
}

해결 방법:

// Flatten or use references
{
  userId: 123,
  profileId: 456
}

3. 대용량 문서

문제점:

// Documents approaching 16MB limit
{
  data: "very large string...",
  attachments: [/* large binary data */]
}

해결 방법:

// Store large data separately (GridFS or object storage)
{
  dataRef: "s3://bucket/key",
  attachments: [{ ref: "gridfs://id" }]
}

1. 연결 풀링을 사용하지 않음

문제점:

// Creating new connection per request
app.get('/api/users', async (req, res) => {
  const client = await MongoClient.connect(uri);
  // ...
  await client.close();
});

해결 방법:

// Reuse connection pool
const client = new MongoClient(uri, { maxPoolSize: 50 });
await client.connect();

app.get('/api/users', async (req, res) => {
  const db = client.db();
  // ...
});

2. 커서를 닫지 않음

문제점:

// Cursor left open
const cursor = db.collection.find();
// Never closed

해결 방법:

// Always close cursors
const cursor = db.collection.find();
try {
  await cursor.forEach(doc => { /* process */ });
} finally {
  await cursor.close();
}

3. 너무 많은 연결

문제점:

// One connection per user session
const connections = new Map();
users.forEach(user => {
  connections.set(user.id, new MongoClient(uri));
});

해결 방법:

// Share connection pool across application
const client = new MongoClient(uri);
// All users share the same pool

1. 인덱스가 너무 많습니다

문제점:

// Index on every field
db.collection.createIndex({ field1: 1 })
db.collection.createIndex({ field2: 1 })
db.collection.createIndex({ field3: 1 })
// ... 20+ indexes

Impact: 쓰기 속도가 느려지고 저장 공간이 증가합니다.

해결책: 필요한 인덱스만 유지하고 복합 인덱스를 사용하세요.

2. 복합 인덱스의 잘못된 인덱스 순서

문제점:

// Query: { status: "active", createdAt: { $gt: date } }
// Index: { createdAt: 1, status: 1 }  // Wrong order

해결 방법:

// Correct order: equality first, range second
db.collection.createIndex({ status: 1, createdAt: 1 })

3. 적용 대상 쿼리를 사용하지 않음

문제점:

// Index exists but query not covered
db.users.createIndex({ email: 1 })
db.users.find({ email: "user@example.com" }, { name: 1, email: 1 })
// Still fetches documents

해결 방법:

// Include all projected fields in index
db.users.createIndex({ email: 1, name: 1 })
db.users.find({ email: "user@example.com" }, { name: 1, email: 1, _id: 0 })

CPU 경고

Condition: CPU > 80% for 10 consecutive minutes
Action: Send notification to ops team
Escalation: Page on-call if > 90% for 15 minutes

메모리 경고

Condition: Memory > 85% for 15 consecutive minutes
Action: Send notification to ops team
Escalation: Auto-scale if > 95% for 10 minutes

복제 지연 경고

Condition: Lag > 10 seconds
Action: Send notification immediately
Escalation: Page on-call if > 60 seconds

디스크 공간 경고

Condition: Disk > 80%
Action: Send notification to ops team
Escalation: Create incident if > 90%